Bickerstaffe Blog - Watts Vs Lumens
What's loomin' in lightin'?
Yes, very funny, Simon. I'm sure regular readers (both of you) are up with the game by now. This is the bit where I try and tell you something illuminating (you see it's quite irresistible) about the wonderful world of LEDs in an undoubtedly hilarious way.
Well, this month it's watts and lumens. (As an English Graduate (scl!) from the esteemed University of Bangor (where?) I don't think that was a particularly well structured sentence - but what can you do? I blame Rupert Murdoch.) The estivators among you may not have noticed that we have all suffered a bereavement this week. Yes, indeed, the bally old EU has killed off the 100 Watt incandescent bulb. It was a dignified death of a very old friend; perhaps two hundred years from the spark of the idea (sorry) to today's ultimate snuffing. Bit of a tricky one to say for sure who invented it -Humphrey Davy with his arc light, Henric Globel, Thomas Alva Edison working with - yes, you've guessed it, bamboo, Swann, Woodward and Evans. Who knows? It depends on your definition of a light bulb I suppose. I mean, if it glows low for a few minutes and then burns out is that technically worthy of the name? A barbecue does a far better job. If you want my view (don't...!), I reckon that the modern light bulb started with the development of the ductile tungsten filament - and that was in 1906 or thereabouts. Queen Victoria wouldn't have seen it but young Bertie, (that's Edward VII to the thickies out there) certainly would and the Royal Family have been at the sharp end of lighting developments ever since. I wonder how many of you knew that the current heir to the throne oversaw the installation of LED lighting several years ago in inaccessible parts of Buckingham Palace, and let's be honest, with those ceilings that's everywhere, to light priceless paintings in the stairwells. Think of the savings on scaffolding bills to change a traditional bulb. His niece could have bought another horse.............shoe.
I'm digressing here I can tell. I sound like Ronnie Corbett. Where's my Pringle sweater?
Yes, watts and lumens. As well as axing the 100 watt bulb the Eurocrats have also told us that we must now deal in lumens and not watts. Shame...scandal...never, I hear both of you cry. But alas here, gentle reader, is where I prefer to take the road less travelled; I think it's an improvement. It's by no means the perfect measure but it is better. There, I've said it. Anyone still reading?
Watts are a measure of electrical consumption. Lumens are a measure of light intensity or, more prosaically, the brightness of something. And surely, if we're talking about lights, that's what you'd prefer to know about, wouldn't you? I mean, an oven uses watts too, but it's more relevant to know how hot it is, don't you think?
The reason it's not perfect is that measuring lumens doesn't tell you about efficiency; how effectively a light source burns relative to the amount of power it's consuming - carbon footprint and all that. On the side of a box in your local supermarket you'll now see 600 lm or 500 lm instead of 60 or 100 watts or whatever. But the key measurement is neither lumens nor watts. It's lumens per watt and by this measurement LEDs win every time. They clearly use the least amount of energy for the most amount of light. A standard LED generates 70+ lumens per watt against a CFL at around 50, a halogen at about 20 and an incandescent at about 15.
The complexities of lux, candela and foot candles and their relationship to visible usable light I'll leave to next month. Bet you can't wait.